Impurity Weight Measurement

ABSTRACT

A method for measuring the weight of impurities in a mixed volume of fibers and impurities by mechanically separating the impurities are from the fibers, whereupon some undesired fibers still remain admixed to the impurities due to imperfections of the mechanical separation. A total weight of the separated impurities and the undesired fibers is gravimetrically measured. An image of the separated impurities and the undesired fibers is created. A weight of the undesired fibers is estimated from the image. The estimated weight of the undesired fibers is subtracted from the total weight to yield a corrected weight of the impurities. The mechanical separation and the subsequent electronic correction yield a more accurate weight of the impurities.

FIELD

This application claims all rights and priority on prior pending patentapplications U.S. Ser. No. 12/774,763 filed May 6, 2010,CN201010180707.7 filed May 6, 2010, and PCT/CH2011/000107 filed May 5,2011. The present invention relates to the field of fiber processing.More particularly, it relates to a method and an apparatus for measuringthe weight of impurities in a mixed volume of fibers and impurities. Oneembodiment is the measurement of the impurity content in raw cotton.

BACKGROUND

Currently in the textile industry, it is usually necessary to measurethe fiber impurity content in raw cotton. The impurity content means theratio of undesired impurities such as sand, branches and leaves, bollhull, and soft seed skin in the fiber. For example, the impurity contentof saw ginned cotton according to the Chinese National Standard is 2.5%.A raw cotton impurity analyzer is generally used in actual work tomeasure the raw-cotton impurity content. As the term is used herein,“impurities” refers to any non-primary-fiber material, such as husks,twigs, leaves, dirt, rocks, and any other non-primary-fiber materialthat might become mixed into the fiber volume. In other publications,the term “trash” is used as a synonym for “impurities.” In the case ofcotton fibers for example, “impurities” refers to anything that isn'tcotton fiber.

A test analysis instrument with a single taker-in cylinder mechanism,e.g. YG041, YG042, and Y101 as described in Chinese National Standard(GB/T0499) “Testing methods for the trash contents of raw cotton,” isadopted in all the traditional test methods for raw cotton impuritycontent. The typical structure of these traditional raw cotton impurityanalyzers is the following: first there is a cotton feeding roller,behind which is a taker-in cylinder, along the circumference of whichare installed two or more separation knives; then there is an aircurrent channel for stripping and taking away the fibers on the surfaceof the taker-in cylinder; and below the separation knife is an impuritydisk that is used for collecting impurities and can be taken outmanually.

The mechanical impurity-separation principle applied in the knowninstruments is the following: the raw cotton is rolled up by the cottonfeeding roller and brought into contact with the taker-in cylinder. Thetaker-in cylinder rotates at a high speed and combs the raw cotton. Thefibers and the impurities, being loosened after being combed by thesawtooth structure on the surface of the taker-in cylinder, adhere tothe surface of the taker-in cylinder under the action of an air current,and rotate at a high speed along with the taker-in cylinder. Due to thedifferent shapes, masses and densities of the fibers and the impurities,under the combined action of the centrifugal force and the air current,the fibers adhere to the surface of the taker-in cylinder, while theimpurities are floated in the air current layer farther away from thesurface of the taker-in cylinder. When passing across the separationknife, the impurities are blocked and fall down to the impurity diskunder the action of gravity, while the fibers continue to rotate withthe taker-in cylinder. When the fibers continuing to rotate with thetaker-in cylinder are brought into the air current channel tangent tothe rotating direction of the taker-in cylinder, due to the pressurechange resulting from the special shape of the air current channel, thefibers are detached from the surface of the taker-in cylinder, and takenaway by the air current.

During the above-mentioned impurity separation process, under the actionof machinery and the air current, a small amount of fibers mayinevitably be detached from the surface of the taker-in cylinder andfall onto the impurity disk. In the traditional impurity analyticalapparatus, the weight content of impurities in the raw cotton can beobtained through manual picking and weighing of the fibers admixed tothe impurities. This manual picking method will not only waste a greatdeal of manpower and time, but also its results show personaldifferences resulting from the personal picking, causing a deviation inthe measured value.

The publication EP-0'533'079 A2 gives an example of an aeromechanicalseparation of impurities from fibers, as applied in the fiber-testingsystem USTER® AFIS PRO 2 from Uster Technologies AG, Uster, Switzerland.The weight of the mixed volume of fibers and impurities is measured byweighing on scales. Then the mixed volume is formed into a sliver, andthe sliver is delivered to a first pinned separator wheel. A secondpinned separator wheel is located below the first separator wheel. Theseparator wheels have each a radius of about 32 mm and rotate at veryhigh speeds of 7000-8000 rpm (i.e., 117-133 s⁻¹). Due to the largecentrifugal forces generated at such high rotational speeds, theimpurities are centrifuged from the surfaces of the separator wheelsinto a counterflow of air. The counterflow air returns fibers back tothe separator wheels, but is overcome by the impurities. The thusseparated impurities are optically sensed by an optical sensor. Acomputer receives the weight data from the scales and the output signalfrom the optical sensor. It calculates the weight of the impurities fromthe accumulated projected area of the impurities. The fibers may beprocessed in the same way as the impurities. This method also suffersfrom the drawback that the mechanical separation may be incomplete.

In summary, the conventional analysis instruments and methods haveshortcomings such as low efficiency and great labor load; besides, twoanalysis cycles on the test sample are generally required in the testanalysis process, with the lower analysis efficiency; moreover, theseparated impurities usually contain effective cotton fibers, whichresults in a deviation in the test result and requires manual picking,thus still resulting in a personal difference in the test result.

SUMMARY

A purpose of the embodiments according to the present invention is toprovide an apparatus and a method for measuring the weight of impuritiesin a mixed volume of fibers and impurities, which not only increaseefficiency and accuracy of the measurement to a great extent, but alsoreduce the labor load.

The above problem is solved by the method and the apparatus as definedin the independent claims. Additional embodiments are defined in thedependent claims.

Any mechanical separation of the impurities from the fibers in the mixedvolume is potentially imperfect, since some undesired fibers will stillremain admixed to the impurities after separation. Therefore, theembodiments according to the invention propose to mechanically separatethe impurities from the fibers, to weigh the separated impurities andthe undesired fibers, and to subsequently correct the measured weigh bymeans of image processing. In this manner, the weight can be correctedby electronic means. This yields a more accurate weight of theimpurities.

In the inventive method for measuring the weight of impurities in amixed volume of fibers and impurities, the impurities are mechanicallyseparated from the fibers, whereupon some undesired fibers still remainadmixed to the impurities due to imperfections of the mechanicalseparation. A total weight of the separated impurities and the undesiredfibers is gravimetrically measured. An image of the separated impuritiesand the undesired fibers is created. A weight of the undesired fibers isestimated from the image. The estimated weight of the undesired fibersis subtracted from the total weight to yield a corrected weight of theimpurities.

In one embodiment, an air current is provided for the mechanicalseparation. The mixed volume is fed onto a surface of a rotating primarytaker-in cylinder located in the air current. The impurities aremechanically striped off from the fibers on the primary taker-incylinder. Part of the mixed volume is transferred from the primarytaker-in cylinder to a secondary taker-in cylinder located in the aircurrent. The impurities are separated from the fibers on the secondarytaker-in cylinder. The impurities separated on the primary taker-incylinder and the secondary taker-in cylinder are collected.

The separation of the impurities from the fibers on the primary taker-incylinder and the secondary taker-in cylinder may make use of the actionof centrifugal force, gravity, the air current and mechanical stripping.

In one embodiment, the primary taker-in cylinder has a diameter of 20-30cm, and in another of 25 cm, and the secondary taker-in cylinder has adiameter of 10-20 cm, and in another of 16 cm. The primary taker-incylinder rotates at a rotational speed of 1300-1700 rpm (21.7-28.3 s⁻¹),and in another embodiment at 1500 rpm (25.0 s⁻¹). The secondary taker-incylinder rotates at a rotational speed of 900-1200 rpm (15.0-20.0 s⁻¹),and in another embodiment at 1050 rpm (17.5 s⁻¹). The primary taker-incylinder has a surface linear velocity of 15-25 m/s, and in anotherembodiment of 19.7 m/s, and the secondary taker-in cylinder has asurface linear velocity of 5-12 m/s, and in another embodiment of 8.7m/s. The centrifugal acceleration on the surface of the primary taker-incylinder is 1860-4740 m/s², and in another embodiment of 3090 m/s², andthe centrifugal acceleration on the surface of the secondary taker-incylinder is 444-1580 m/s², and in another embodiment of 967 m/s². Thesecentrifugal accelerations are clearly lower than those on the surfacesof the separator wheels as described in EP-0'533'079 A2, wheremechanical stripping devices are not used.

In some embodiments the surface of at least one of the primary taker-incylinder and the secondary taker-in cylinder bears a serrated structureor sawtooth structure. The primary taker-in cylinder and the secondarytaker-in cylinder may have the same rotational direction.

In one embodiment, the air current below the taker-in cylinders hasessentially a horizontal direction. Such a horizontal air current actslike a sheet of air that carries away fibers detached from the taker-incylinders. The impurities, which are heavier than the fibers, fallthrough this sheet of air under the action of gravity.

The inventive apparatus for measuring the weight of impurities in amixed volume of fibers and impurities comprises a separation device formechanically separating the impurities from the fibers, a gravimetricscale for measuring a total weight of the separated impurities andundesired fibers remaining admixed to the impurities, and a sensor forcreating an image of the separated impurities and the undesired fibers.The apparatus further comprises a processor for detecting undesiredfibers within the image, estimating a weight of the undesired fibersfrom the image, and subtracting the estimated weight of the undesiredfibers from the total weight to yield a corrected weight of theimpurities.

In one embodiment, the separation device comprises an air currentchannel, a fiber feeding device located at a front end of the aircurrent channel, a primary taker-in cylinder located in the air currentchannel behind the fiber feeding device, and at least one stationarystripping device located near the surface of the primary taker-incylinder. A secondary taker-in cylinder is located in the air currentchannel behind the primary taker-in cylinder, surfaces of the primarytaker-in cylinder and the secondary taker-in cylinder being adjacent toeach other. An impurity collecting apparatus is located below theprimary taker-in cylinder and the secondary taker-in cylinder. In oneembodiment the impurity collecting apparatus is connected to thegravimetric scale.

The primary taker-in cylinder and the secondary taker-in cylinder in oneembodiment are mutually arranged such that part of the mixed volume istransferrable from the primary taker-in cylinder to the secondarytaker-in cylinder. In one embodiment, the minimum distance between thesurfaces of the taker-in cylinders is between 0.1 and 1 mm, and inanother embodiment is 0.25 mm. The primary taker-in cylinder has adiameter of 20-30 cm, and in another embodiment is 25 cm, and thesecondary taker-in cylinder has a diameter of 10-20 cm, and in anotherembodiment is 16 cm.

In one embodiment, the separation device comprises a drive mechanism forthe primary taker-in cylinder, which drive mechanism is adapted fordriving the primary taker-in cylinder at a rotational speed of 1300-1700rpm (21.7-28.3 s⁻¹), and in another embodiment of 1500 rpm (25.0 s⁻¹).Likewise, the separation device comprises a drive mechanism for thesecondary taker-in cylinder, which drive mechanism is adapted fordriving the secondary taker-in cylinder at a rotational speed of900-1200 rpm (15.0-20.0 s⁻¹), and in another embodiment of 1050 rpm(17.5 s⁻¹). At least one of the primary taker-in cylinder and thesecondary taker-in cylinder may have a width in axial direction of 30-70cm, and in another embodiment of 50 cm. The surface of at least one ofthe primary taker-in cylinder and the secondary taker-in cylinder maybear a serrated structure or sawtooth structure. Such serrated surfacesare more aggressive than the pinned surfaces known from the prior art,and thus more effectively separate the impurities from the fibers. Apotential damaging of the fibers is irrelevant in the presentapplication. The height of the serrated structure may be 1-4 mm, and inanother embodiment is 2.5 mm.

The apparatus according to the embodiments of the invention is thus ableto process 30 grams of sample per minute, whereas the apparatusaccording to EP-0'533'079 A2 processes only 0.25 grams per minute. Thehigh processing capacity makes the apparatus according to the inventionsuitable for high-volume fiber processing.

At least one additional stationary stripping device may be located nearthe surface of the secondary taker-in cylinder. The distance between theat least one stripping device and the surface of the respective taker-incylinder is between 0.1 mm and 1 mm, and in another embodiment isbetween 0.2 and 0.6 mm.

The fiber feeding device preferably includes a fiber feeding roller anda fiber feeding plate.

Thanks to the embodiments according to the present invention, the mixedvolume does not need to be painstakingly separated in sometime-consuming or labor-consuming process. Nor does the weight need tobe compromised by the weight of undesired fibers. Thus, a correctedweight that accurately represents the impurities can be quickly, easily,and automatically generated. After the preferred double impurity removalwith the primary taker-in cylinder and the secondary taker-in cylinder,the impurities are removed from the cotton sample more completelycompared to the prior-art single taker-in cylinder structure, making thesubsequent impurity measurement value more accurate. Therefore,efficiency and accuracy of the measurement is increased significantly.

DRAWINGS

Embodiments of the present invention are further described below indetail with reference to the drawings.

FIG. 1 shows a functional block diagram of the apparatus according to anembodiment the invention.

FIG. 2 shows a functional block diagram of the impurity separationsection of the apparatus according to an embodiment the invention.

FIG. 3 shows a schematic front view of part of a taker-in cylinderincluded in the apparatus according to an embodiment the invention.

FIG. 4 shows a functional block diagram of the weight-determiningsection of the apparatus according to an embodiment the invention.

FIG. 5 shows a flow chart of an embodiment of the method according tothe invention.

DESCRIPTION

As can be seen in FIG. 1, the apparatus according to the inventioncomprises a fiber feeding device comprising a fiber feeding roller 1 anda fiber feeding plate 2, the fiber feeding roller 1 feeding the rawcotton sample (not shown) that needs an impurity test. The raw cottonsample, gripped by the fiber feeding roller 1 and the fiber feedingplate 2, is combed by a primary taker-in cylinder 5 and a secondarytaker-in cylinder 6. The mechanical separation of the impurities fromthe fibers is described in more detail below with reference to FIGS. 2and 3.

An impurity disk 8 is positioned below the taker-in cylinders 5, 6. Theimpurities that are combed out fall downwards to the impurity disk 8.The impurity disk 8 is big enough such that all the impurities separatedfrom the taker-in cylinders 5, 6 are collected on the impurity disk 8.An electronic scale 9 is positioned below the impurity disk 8 and insome embodiments is connected to it. The impurities, falling to theimpurity disk 8 when passing across the taker-in cylinders 5, 6, areweighed automatically by the electronic scale 9 after sample completion.

In most cases the separation of the impurities from the fibers isimperfect, so that some undesired fibers are still admixed to theimpurities on the impurity disk 8. Therefore, the weight measured by theelectronic scale 9 is higher than the actual weight of the impurities.The invention proposes to correct the weight, as described in thefollowing. A digital camera 12 takes images of the impurities andundesired fibers on the impurity disk 8. The digital camera 12 and theelectronic scale 9 are both connected to a processor 13. The processor13 analyzes the image provided by the digital camera 12 and estimatesthe weight of the undesired fibers admixed to the impurities by means ofimage processing. Then it corrects the measured weight by subtractingfrom it the estimated weight of the undesired fibers. The weightcorrection is described in more detail below with reference to FIGS. 4and 5.

FIG. 2 shows in more detail the mechanical impurity separation sectionof the apparatus according to the present invention. It includes an aircurrent channel which comprises an air current guide 7. The fiberfeeding device 1, 2 and the taker-in cylinders 5, 6 are arranged in theair current. The directions of the air current at various locations areindicated by arrows. The air current below the taker-in cylinders 5, 6has an essentially horizontal direction. The black dots shown in FIG. 2indicate the impurities 11 that are combed out, some of the impurities11 falling downwards to the impurity disk 8 under the combined action ofgravity and centrifugal force.

Primary separation knives 3.1, 3.2 are positioned in a stationary manneralong and near the surface of the primary taker-in cylinder 5. Theabove-mentioned impurities adhering to the taker-in cylinder 5, whenpassing across the primary separation knives 3.1, 3.2, are blocked bythe separation knives 3.1, 3.2 and fall down to the impurity disk 8.Thus, the separation knives 3.1, 3.2 act as stripping devices that stripoff or comb out the impurities. There are one or more such separationknives 3.1, 3.2, the amount being determined as required. The linearsurface velocity v (see FIG. 3) of the primary taker-in cylinder 5according to the invention is significantly higher, e.g., nearly twiceas high, than that of the taker-in cylinder in a traditional analyticalapparatus. It is within the range of 15-25 m/s in one embodiment, and inanother embodiment of 17.7-21.7 m/s, and in another embodiment is 19.7m/s.

According to the embodiments of the present invention, behind theprimary taker-in cylinder 5 is positioned the secondary taker-incylinder 6, whose surface is near but not in direct contact with thesurface of the primary taker-in cylinder 5. The secondary taker-incylinder 6 rotates more slowly than the primary taker-in cylinder 5; itslinear surface velocity v in one embodiment is within 5-15 m/s, and inanother embodiment within 7.5-9.9 m/s, and in another embodiment is 8.7m/s. The secondary taker-in cylinder 6 has the same rotational directionas the primary taker-in cylinder 5. In the region where the surfaces ofthe taker-in cylinders 5, 6 have minimum distance, the surface speedvectors of the taker-in cylinders 5, 6 are opposed to each other and therelative linear surface velocity equals the sum of the two velocities.The fibers are transferred from the primary taker-in cylinder 5 to thesecondary taker-in cylinder 6.

The cotton fibers, after being combed, are attached to the surface ofthe primary taker-in cylinder 5 and move with it and, when passing theregion where the surfaces of the taker-in cylinders 5, 6 have minimumdistance, are combed again by the secondary taker-in cylinder 6. Thus,impurities not combed out by the separation knives 3.1, 3.2 are combedout by the secondary taker-in cylinder 6. In addition, a secondaryseparation knife 4 may be assigned to the secondary taker-in cylinder 6;the secondary separation knife 4 and the secondary taker-in cylinder 6cooperate as described for the primary separation knives 3.1, 3.2 andthe primary taker-in cylinder 5 in order to strip off the remainingimpurities. As mentioned above, the impurities 11 fall to the impuritydisk 8 under the action of gravity and centrifugal force. Thus, theinvention, after double impurity removal with the primary taker-incylinder 5 and the secondary taker-in cylinder 6, removes the impuritiesfrom the cotton sample more completely compared to the prior-art singletaker-in cylinder structure, making the subsequent impurity measurementvalue closer to the actual value.

The cotton fibers, on the other hand, continue to rotate with thetaker-in cylinders 5, 6. When the air current is tangent to thesurface-velocity vector of the respective taker-in cylinder 5, 6, theyexperience a pressure drop. The fibers are then detached from thesurface of the respective taker-in cylinder 5, 6, and taken away by theair current.

The secondary taker-in cylinder 6 can be designed to have the samestructure as the primary taker-in cylinder 5. For example, two or moreseparation knives, the amount being determined as required, can bepositioned along the surface of the secondary taker-in cylinder 6.

The primary taker-in cylinder 5 has a diameter 2 r (see FIG. 3) in oneembodiment of 20-30 cm, and in another embodiment of 25 cm, and thesecondary taker-in cylinder 6 has a diameter 2 r in one embodiment of10-20 cm, and in another embodiment of 16 cm. The widths in axialdirection of the taker-in cylinders 5, 6 in one embodiment are 30-70 cm,and in another embodiment are 50 cm. The minimum distance between thesurfaces of the taker-in cylinders 5, 6 in one embodiment is between 0.1and 1 mm, and in another embodiment is 0.25 mm. The distance betweeneach of the separation knives 3.1, 3.2, 4 and the surface of the primarytaker-in cylinder in one embodiment is between 0.1 and 1 mm, and inanother embodiment is between 0.2 mm and 0.6 mm.

FIG. 3 shows a schematic front view, not to scale, of part of thetaker-in cylinder 5 or 6. The radius r of the taker-in cylinder 5, 6 inone embodiment is in the range between 5 and 15 cm. The surface of thetaker-in cylinder 5, 6 bears a serrated structure 10 built up, e.g., ofa sequence of saw teeth equally distributed along the circumference ofthe taker-in cylinder 5, 6. In one embodiment the height h of theserrated structure is in the range between 1 and 4 mm, i.e., the ratioof the height h and the radius r is in the range between 0.7% and 8%.The serrated structure 10 extends over essentially the whole width ofthe taker-in cylinder 5, 6. This may be realized by a serrated band thatwraps the lateral area of the cylinder 5, 6 in the form of a helicalcurve. The angular speed w of the taker-in cylinder 5, 6 in oneembodiment is in the range between 94.3 rad/s and 178 rad/s. The surfacevelocity v can be calculated according to the formula:

v=ωr,

and the centrifugal acceleration a is given by the formula:

a=ω²r.

The embodiments of present invention can be applied to the impuritymeasurement in raw cotton and other fiber products. The embodimentsdiscussed above have a primary taker-in cylinder 5 and a secondarytaker-in cylinder 6. Depending on the actual application, based on theconception of the present invention, a third taker-in cylinder, a fourthtaker-in cylinder and so on can be provided, with their surfacesconsecutively near to each other and their structure being similar tothat according to the embodiment discussed above. The total number N oftaker-in cylinders is a positive integer bigger than or equal to 2.

The fibers, after being combed by the primary taker-in cylinder 5, canbe combed again by the secondary taker-in cylinder 6 according to theinvention, which can comb out more impurities that are not combed outduring the first impurity removal process. For example, the apparatusaccording to the above embodiment of the invention can complete theimpurity weight content analysis of a 30-gram raw cotton sample withinone minute. Its efficiency is increased by a factor of 3.5 compared withthe traditional raw cotton impurity content analysis instruments.Meanwhile, with the introduction of a camera system, the analysisaccuracy of raw cotton impurity content is increased to a great extent,and the labor load reduced at the same time.

In FIG. 4, there is depicted a functional block diagram of aweight-determining section of the apparatus according to the invention.The impurity disk 8 receives the volume in which impurities 11 are to beweighed. In the example as depicted, the volume is comprised ofcomponents 11, 14 and 15. For example, the volume might includeimpurities 11, an unknown object 14, and fibers 15. The electronic scale9 measures the total weight of the volume, and provides the total weightto the processor 13 for further analysis. The camera 12 records an imageof the volume on the impurity disk 8 within a field of view 16, andprovides the image to the processor 13 for further analysis. Theprocessor 13 implements the algorithm as described below, and determinesthe corrected weight, as desired.

With reference now to FIG. 5, there is depicted a flow-chart of a methodaccording to the invention. As given in block 101, the impurities 11 aremechanically separated from the fibers 15, albeit incompletely, so thatsome undesired fibers 15 are admixed to the impurities 11. The separatedimpurities 11 and the remaining undesired fibers 15 are weighed, asgiven in block 102. This weight can be accomplished in a variety ofdifferent ways. For example, the separated impurities 11 and theremaining undesired fibers 15 can be directly weighed with a gravimetricdevice like a scale 9. Whatever method is used, this initial weight ofthe mixed volume is designated herein as the total weight.

An image is then created of the volume on the impurity disk 8, as givenin block 103. In some embodiments, the volume is scattered across asurface, such that all components of the mixed volume can be readilyseen from one direction, such as from above the volume. In this manner,the individual components of the mixed volume are not hidden, one byanother, from the view-point of the camera 12. In some embodiments asingle optical visible-light image from a single camera 12 at a singlelocation is used to create the image of the volume. In otherembodiments, multiple images from multiple sensors at multipleorientations are created, and in some embodiments wavelengths other thanvisible wavelengths are used to create the image or images. In stillother embodiments, three-dimensional or quasi-three-dimensional imagingtechniques such as tomography are applied. Other combinations ofproperties such as these are also contemplated.

Once the image has been obtained, as given in block 103, an algorithm isperformed using the image as an input. The algorithm discriminates thevarious components of the image, as given in block 104. By“discriminates” it is meant that the various components 11, 14, 15 ofthe volume as depicted in the image are identified as to classification.For instance, those portions of the image that represent fibers 15 areidentified as one classification, and those portions of the image thatrepresent impurities 11 are identified as another classification.

The algorithm can be adapted so as to identify more than two classes ofcomponents 11, 14, 15 within the volume, as desired. Various thresholdlevels can be set as desired so as to make the determination as to how agiven portion of the image should be classified. Because in someembodiments the volume does not completely cover the surface upon whichis it disposed, the algorithm can be set, in those embodiments, toexclude from classification those portions of the surface that arevisible in the image, as desired.

Once the image has been classified, the weight of at least those classesof material that do not relate to impurities 11 is estimated, as givenin block 105, such as by the algorithm. In some embodiments, the weightsof all of the classes of material within the volume are estimated, orthe weights of some variable number of the classes are estimated. Thiscan be accomplished by, for example, determining from the image thetotal volume of fibers 15 within the volume, and then multiplying thattotal volume by a presumed or measured fiber density value. A variety ofdifferent algorithms for determining the weight of the fibers 15 couldbe used in different embodiments. These determined weights aredesignated as the component weights.

After the weight of at least one component of the volume has beenestimated, the corrected weight of the impurities is determined, asgiven in bock 106, such as by subtracting one or more of the componentweights from the total weight. For example, the component weight of thefibers 15 can be subtracted from the total weight, yielding a correctedweight of impurities 11.

It is appreciated that some of the steps of the embodiment of the methodas described above do not need to be performed in the order as describedabove or depicted in FIG. 5. For example, measuring the total weight ofthe mixed volume, as represented in block 102, does not need to beaccomplished prior to imaging the mixed volume and estimating thecomponent weight or weights, as given in blocks 103-105. However, thesteps of measuring the total weight 102 and estimating at least onecomponent weight 105 do need to be accomplished prior to determining thecorrected weight 106. In some embodiments, these steps of measuring thetotal weight 102 and estimating at least one component weight 105 areaccomplished substantially simultaneously.

The present invention is not limited to the embodiments discussed above.The descriptions of the embodiments above are only for describing andexplaining the technical solution involved in the invention. An obvioustransformation and substitution based on the present invention shouldalso be thought to be within the scope of protection of the invention.The embodiments above are used to enable those skilled in the art toachieve the purpose of the present invention by using variousembodiments and various substitute methods.

REFERENCES

-   1 Fiber feeding roller-   2 Fiber feeding plate-   3.1, 3.2 Primary separation knives-   4 Secondary separation knife-   5 Primary taker-in cylinder-   6 Secondary taker-in cylinder-   7 Air current guide-   8 Impurity disk-   9 Electronic scale-   10 Serrated structure-   11 Impurities-   12 Sensor-   13 Processor-   14 Unknown object-   15 Fiber-   16 Field of view-   101 Mechanical separation-   102 Total weight measurement-   103 Image creation-   104 Image discrimination-   105 Fiber weight estimation-   106 Weight correction-   h Height of the serrated structure-   r Radius of the taker-in cylinder-   v Surface linear velocity of the taker-in cylinder-   ω Rotational speed of the taker-in cylinder

1. A method for measuring a weight of impurities in a mixed volume offibers and impurities, comprising the steps of: mechanically separatingthe impurities from the fibers, some undesired fibers still remainingadmixed to the impurities due to imperfections of the mechanicalseparation, gravimetrically measuring a total weight of the separatedimpurities and the undesired fibers, creating an image of the separatedimpurities and the undesired fibers, estimating a weight of theundesired fibers from the image, and subtracting the estimated weight ofthe undesired fibers from the total weight to yield a corrected weightof the impurities.
 2. The method according to claim 1, wherein themechanical separation comprises the steps of: providing an air current,feeding the mixed volume onto a surface of a rotating primary taker-incylinder located in the air current, mechanically stripping off theimpurities from the primary taker-in cylinder, transferring part of themixed volume from the primary taker-in cylinder to a secondary taker-incylinder located in the air current, separating the impurities from thefibers on the secondary taker-in cylinder, and collecting impuritiesseparated on the primary taker-in cylinder and the secondary taker-incylinder.
 3. The method according to claim 2, wherein the primarytaker-in cylinder has a diameter of at least one of 20-30 cm and 25 cm,and the secondary taker-in cylinder has a diameter of at least one of10-20 cm and 16 cm.
 4. The method according to claim 2, wherein theprimary taker-in cylinder rotates at a rotational speed of at least oneof 1300-1700 rpm and 1500 rpm, and the secondary taker-in cylinderrotates at a rotational speed of at least one of 900-1200 rpm and 1050rpm.
 5. The method according to claim 2, wherein the primary taker-incylinder has a surface linear velocity of at least one of 15-25 m/s and19.7 m/s, and the secondary taker-in cylinder has a surface linearvelocity of at least one of 5-12 m/s and 8.7 m/s.
 6. The methodaccording to claim 2, wherein the centrifugal acceleration on thesurface of the primary taker-in cylinder is at least one of 1860-4740m/s² and 3090 m/s², and the centrifugal acceleration on the surface ofthe secondary taker-in cylinder is at least one of 444-1580 m/s² and 967m/s².
 7. The method according to claim 2, wherein the surface of atleast one of the primary taker-in cylinder and the secondary taker-incylinder bears a serrated structure.
 8. The method according to claim 2,wherein the primary taker-in cylinder and the secondary taker-incylinder have the same rotational direction.
 9. The method according toclaim 2, wherein the air current below the taker-in cylinders hasessentially a horizontal direction.
 10. An apparatus for measuring theweight of impurities in a mixed volume of fibers and impurities,comprising: a separation device for mechanically separating theimpurities from the fibers, a gravimetric scale for measuring a totalweight of the separated impurities and undesired fibers remainingadmixed to the impurities, a sensor for creating an image of theseparated impurities and the undesired fibers, and a processor for:detecting the undesired fibers within the image, estimating a weight ofthe undesired fibers from the image, and subtracting the estimatedweight of the undesired fibers from the total weight to yield acorrected weight of the impurities.
 11. The apparatus according to claim10, wherein the separation device comprises: an air current channel, afiber feeding device located at a front end of the air current channel,a primary taker-in cylinder located in the air current channel behindthe fiber feeding device, at least one stationary stripping devicelocated near the surface of the primary taker-in cylinder, a secondarytaker-in cylinder located in the air current channel behind the primarytaker-in cylinder, surfaces of the primary taker-in cylinder and thesecondary taker-in cylinder being adjacent to each other, and animpurity collecting apparatus located below the primary taker-incylinder and the secondary taker-in cylinder.
 12. The apparatusaccording to claim 11, wherein the primary taker-in cylinder and thesecondary taker-in cylinder are mutually arranged such that part of themixed volume is transferrable from the primary taker-in cylinder to thesecondary taker-in cylinder.
 13. The apparatus according to claim 11,wherein the minimum distance between the surfaces of the taker-incylinders is at least one of 0.1-1 mm and 0.25 mm.
 14. The apparatusaccording to claim 11, wherein the primary taker-in cylinder has adiameter of at least one of 20-30 cm and 25 cm, and the secondarytaker-in cylinder has a diameter of at least one of 10-20 cm and 16 cm.15. The apparatus according to claim 14, wherein the separation devicecomprises a drive mechanism for the primary taker-in cylinder, the drivemechanism for driving the primary taker-in cylinder at a rotationalspeed of at least one of 1300-1700 rpm and 1500 rpm, and the separationdevice comprises a drive mechanism for the secondary taker-in cylinder,the drive mechanism for driving the secondary taker-in cylinder at arotational speed of at least one of 900-1200 rpm and 1050 rpm.
 16. Theapparatus according to claim 11, wherein at least one of the primarytaker-in cylinder and the secondary taker-in cylinder has a width inaxial direction of at least one of 30-70 cm and 50 cm.
 17. The apparatusaccording to claim 11, wherein the surface of at least one of theprimary taker-in cylinder and the secondary taker-in cylinder bears aserrated structure.
 18. The apparatus according to claim 17, wherein theheight of the serrated structure is at least one of 1-4 mm and 2.5 mm.19. The apparatus according to claim 11, wherein at least one additionalstationary stripping device is located near the surface of the secondarytaker-in cylinder.
 20. The apparatus according claim 11, wherein thedistance between the at least one stripping device and the surface ofthe respective taker-in cylinder is at least one of 0.1-1 mm and 0.2-0.6mm.
 21. The apparatus according to claim 11, wherein the fiber feedingdevice includes a fiber feeding roller and a fiber feeding plate.